The present invention relates to a method for forming a phase-shifting mask for the production of semiconductor devices and, more particularly, to a method for improving the lithographic resolution using a multi-transmittance phase-shifting mask
Generally, each level of semiconductor device circuitry is first generated on one or more photomasks that are, in turn, used in order to form the corresponding circuitry on a wafer surface. Typically, a series of reticles are generated in pattern generation works from the recorded circuit design data and, a master mask is then formed using the reticles. Attenuated phase-shifting masks used in DRAM fabricating processes, may be broadly classified into two types based on the way in which they are used. The first type is intended to increase the processing margin for forming linear spaces and the second is intended to increase the depth of focus for forming contact holes.
FIGS. 1A and 1B provide plan and cross-sectional views illustrating conventional attenuated phase-shifting masks. The upper figure is the cross-sectional view taken along the line Axe2x80x94A in the lower figure. In the drawings, chromium patterns 11 are formed on predetermined area of a quartz substrate 10. Further, FIG. 1A illustrates a conventional attenuated phase-shifting mask for forming fine patterns of lines and spaces with an expected processing margin.
FIG. 1B, however, illustrates a conventional attenuated phase-shifting mask for forming contact holes. The upper figure is the cross-sectional view taken along the line Bxe2x80x94B in the lower figure. Generally, the chromium patterns designed and printed on the quartz substrate 10 are larger than the actual size of the pattern formed on a wafer. That is, the contact hole patterns are formed to provide a depth of focus (DOF) capable of resolving any size differences between mask pattern according to the design and the actual wafer-level patterns.
FIG. 1B shows an attenuated phase-shift mask having a transmittance of about 5 to 9% through the chromium patterns. If an amount of the transmittance level is a little high, interference may be generated by light transmitted through adjacent areas, thereby forming undesired patterns such as ghost images and side lobes. The use of the attenuated phase-shift mask with a low transmittance level, therefore, will tend to improve the resolution of fine patterns by suppressing the undesired patterns.
The size of the mask patterns may be also reduced in order to form correspondingly smaller patterns on the wafer, but the degree to which the size of the mask pattern may be reduced will be limited by design rules associated with the mask forming processes. In particular, with the reduction of the size of the patterns, the processing margin can be reduced so dramatically that both a low transmittance mask and a high transmittance mask are required simultaneously to reproduce a single pattern with the desired accuracy. Accordingly, in those cases where only one mask, either a low transmittance mask or high transmittance mask, is used in the patterning process, the process performance is compromised. Indeed, the benefits of the non-selected mask are simply lost and the pattern produced will be less than optimal.
It is, therefore, an object of the present invention to provide a method for improving resolution in the formation of photoresist patterns by using a multi-transmittance phase-shifting mask having both low transmittance and high transmittance regions.
It is another object of the present invention to improve the processing margin in fabricating semiconductor devices and improve the appearance of photoresist patterns and the resulting semiconductor devices.
In accordance with an aspect of the present invention, there is provided a method for forming a photomask for a semiconductor device, the method comprising the steps of: forming a plurality of light blocking layers and a phase-shifting layer on a transparent substrate; defining at least two different areas that require different transmission levels in order to best pattern the semiconductor device; determining the necessary level of transmission of the exposing light based on the defined areas; and selectively patterning the light blocking layers and the phase-shifting layers using a photoresist layer as an etching mask to control transmittance of exposure light in the defined areas.
In accordance with another aspect of the present invention, there is provided a method for forming a photomask for a semiconductor device, wherein the semiconductor device has a scribe lane, a peripheral circuit area and a cell area, the method comprising the steps of: forming a first stacked structure on the a scribe lane with a first transmittance of 0% for the exposing light, wherein the first stacked structure includes a plurality of light blocking layers; forming a second stacked structure on the peripheral circuit area with a second transmittance for the exposing light, wherein the second stacked structure includes at least one light blocking layer and a phase-shifting layer; and forming a third stacked structure on the cell area with a third transmittance for the exposing light, wherein the third stacked structure includes at least two light blocking layers and a phase-shifting layer.